While searching solution for my Java exception online found very nice explanation on StackOverflow about some basic difference between HashSet and TreeSet.
HashSet is much faster than TreeSet (constant-time versus log-time for most operations like add, remove and contains) but offers no ordering guarantees like TreeSet.
HashSet:
- class offers constant time performance for the basic operations (add, remove, contains and size).
- it does not guarantee that the order of elements will remain constant over time
- iteration performance depends on the initial capacity and the load factor of the HashSet.
- It’s quite safe to accept default load factor but you may want to specify an initial capacity that’s about twice the size to which you expect the set to grow.
TreeSet:
- guarantees log(n) time cost for the basic operations (add, remove and contains).
- guarantees that elements of set will be sorted (ascending, natural, or the one specified by you via it’s constructor).
- doesn’t offer any tuning parameters for iteration performance.
- offers a few handy methods to deal with the ordered set like first(), last(), headSet(), and tailSet() etc.
Important points:
- Both guarantee duplicate-free collection of elements
- It is generally faster to add elements to the HashSet and then convert the collection to a TreeSet for a duplicate-free sorted traversal.
- None of these implementation are synchronized. That is if multiple threads access a set concurrently, and at least one of the threads modifies the set, it must be synchronized externally.
LinkedHashSetis in some sense intermediate between HashSet and TreeSet. Implemented as a HashTable with a linked list running through it, however it provides insertion-ordered iteration which is not same as sorted traversal guaranteed by TreeSet.
So choice of usage depends entirely on your needs but I feel that even if you need an ordered collection then you should still prefer HashSet to create the Set and then convert it into TreeSet.
e.g. Set<String> s = new TreeSet<String>(hashSet);
Some more Java Tutorials to look: https://crunchify.com/category/java-tutorials/